Bifacial solar cells (BSC) may use any of a variety of different designs to achieve higher efficiencies than those typically obtained by a conventional, monofacial solar cell. One such design is shown in U.S. Pat. No. 5,665,175 which discloses a BSC configuration with first and second active regions formed on the front and back surfaces of the BSC, respectively, the two regions separated by a distance λ. The distance λ allows a leakage current to flow between the first and second active regions, thus allowing a solar cell panel utilizing such bifacial cells to continue to operate even if one or more individual solar cells become shaded or defective.
U.S. Pat. No. 7,495,167 discloses an n+pp+ structure and a method of producing the same. In the disclosed structure, the p+ layer, formed by boron diffusion, exhibits a lifetime close to that of the initial level of the substrate. In order to achieve this lifetime, the '167 patent teaches that after phosphorous gettering, the cell must be annealed at a temperature of 600° C. or less for one hour or more. In order to retain the lifetime recovered by the phosphorous and low-temperature born gettering steps, the cell then undergoes a final heat treatment step in which the cell is fired at a temperature of around 700° C. or less for one minute or less.
U.S. Patent Application Publication No. 2005/0056312 discloses an alternative technique for achieving two or more p-n junctions in a single solar cell, the disclosed technique using transparent substrates (e.g., glass or quartz substrates). In one disclosed embodiment, the BSC includes two thin-film polycrystalline or amorphous cells formed on opposing sides of a transparent substrate. Due to the design of the cell, the high temperature deposition of the absorber layers can be completed before the low temperature deposition of the window layers, thus avoiding degradation or destruction of the p-n junctions.
Although there are a variety of BSC designs and techniques for fabricating the same, these designs and techniques tend to be relatively complex, and thus expensive. Accordingly, what is needed is a solar cell design that achieves the benefits associated with bifacial solar cells while retaining the manufacturing simplicity of a monofacial solar cell. The present invention provides such a design.